Production of aluminum hydroxide



. fluorides capable of Patented Nov. 1932' a UNI-TED srarss PATENT OFFICE SVEND S. SV ENDBEN, 0] CHICAGO, ILLINOIS, ABBIGNOR TO CLAY REDUCTION CORPORA- TION, A CORPORATION OF'ILLINOIS PBODYO'I'ION 01' ALUMINUM HYDBOXIDE This invention relates to the production of aluminum hydroxide. It is illustrated in the accompan 'ng drawing, in which a flow sheet showing t e procedure in connection with a .3 specific example of the invention is presented.

In my rior applications Serial No. 191,- 267, filed th 13,1927 and serial No. 242,291. filed December 23, 1927, I have described and claimed processes in which minerals contain- 19 ing silica and alumina, with or without other metallic compounds are treated with ammonium fluoride and the mixture heated to produce and volatilize ammonia silican fluorine compounds, lcavini a residue of metallic eing worked up for valuable productsl The ammonia silicon fluorine compounds are decomposed by treatment with water and ammonia at tem rature below 3*? C. giving h drated silica and ammonium fluoride. is ammonium fluoride is recovered and reused in the process.

In accordance with the present invention minerals containing alumina and silica, with or without alkali metal oxides, are heated with ammonium fluoride or bifluoride or substances which yield the same under the conditions of the reaction and all or a substantial part of the silica is thereby volatilized. The alumina and alkali metal compound if any 0 alkali metals be present, are converted either directly or indirectl into sulfates by the action of reactive fates;

'. By" the term reactive sulfates I intend to designate sulfuric acid, bisulfates, articu- 85 larly bisulfates of ammonium an alkali metals, ammonium shlfate and other sulfates which, undhr the conditions of the reaction part with the sulfate radicals necessary for thm'oduction of the metallic sulfates.

i ere sulfuric acid is employed as the reactive sulfate, it is preferred --to treat the minerals first with ammonium fluoride and I efl'ect the sulfation in a subsequent operation. Where other reactive sulfates are used, they are preferably added to'the minerals under treatment-in thefirst instance.

The ammonium fluoride may be sup lied in the dry state or in solution or in the cm of va or. On heating to about 200 C. to

' W 380 the ammonium fluoride with 7, 192a. sum no. 304,017.

the minerals, the principal reaction being the T roduction of silicon diammino tetrafluoride, iF (NHQ which volatilizes at such tem-' peratures and condenses to a li ht, flufiy sublimate,stable in the presence ofammonia or water vapor. Water and ammonia are also liberated and collected. The silicon fluoride ammonia is treated with water giving at temperatures below about 34 C. ammonium silico-fluoride, ammonium fluoride and' hydrated silica. In the presence of ammonia the dissolved ammonium silicofluoride at temperaturesbelow about 34 C. is quantitativel converted into further hydrated silica an ammonum fluoride. The ammonium fluoride is recovered and reused in the process.

Instead of using ammonium fluoride I may add to the reaction mixture substances which react to reduce ammonium fluoride, for example, uorspar and ammonium sulfate. I prefer to replace mechanical loss of ammonium fluoride in this manner.

The decomposition of the silicates procceds satisfactorily with less fluoride than is necessary to combine with all the silica. However, in this manner of operation, flocculent silica is produced which ham rs the filtration of the lixiviated residue. therefore, prefer to employ anamount of fluoride approximately equivalent to the content of 1 the combined silica. It is to be noted that quartz is substantially unafiected and y be disregarded in the calculation of 1 3- tities.-

The reaction temperature should be maintained below 835 C. to avoid losses 0 a'mmonia and sulfuric acid due to the pr duction of nitrogen and sulfur dioxide. .The reaction mixture is thereby maintained in dry state, i e., in a condition not permitting the presence of liquid water. The reaction with some cla s occurs at a temperature below 250 C. n the treatment 0 other clays much higher temperatures are necessary The tem rature varies however, to some ex tent witg the nature 0 'the' mineral treated. By 0' crating under a slight vacuum, for examp e, a few inches of mercury, the rate of the reaction is enhanceda Where the mineraltreated contains iron,

it is preferably reduced to the ferrous state to avoid the production of ferric alum and also to prevent loss of ammonia during the reaction. This reduction may suitably be effected by passing a reducing gas such as carbon monoxide hydrogen or gases containing them throng i the finely divided mineral at temperatures of the order of 400 C. In

many cases there is sufficient organic matter in the mineral so that the reduction can be effected by mere heating in an inert atmosphere, such as of steam. Where iron is present, it is preferred to avoid any excess of sulfate or to use somewhat less than theoretically required to convert the alumina and alkali metal compounds into sulfates. In this way most of the iron in the residue is in the form of insoluble compounds.

The aluminum sulfate or alums which are extracted from the residue and crystallized may be converted into pure aluminum hydroxide in any suitable manner. I prefer however to effect this conversion by exposing theicrystals of these substances to an atmosphere of ammonia, The ammonia dissolves in the water of crystallization, permeates the crystals and decomposes the aluminum sulfate with the production of aluminum hydroxide and ammonium sulfate. The crystals retain their form. The conversion may be expedited by increasing the pressure of the ammonia gas and cooling the .charge. The reaction proceeds satisfactorily at atmospheric pressure but su er-atmospheric pressures may be employed i desired. Since the reaction is exothermic the charge should be cooled to get rapid conversion.-

The ammonium sulfate formed in this conversion is dissolved in water and the aluminum hydroxide separated by filtering. The

filtrate contains ammonium sulfate with or without alkali metal sulfates which may be recovered and reused in the process. a

The invention will be more completely understood from the following specific examples Example I Pulverized bauxite, in which the ferric compounds have been reduced to ferrous as described above, is mixed with ammonium fluoride suflicient to convert the silica content into silicon diammino tetrafluoride (SiF,(NH,),) and with ammonium sulfate suflicient to convert the alumina content into ammonium aluminum sulfate and a little less than sufficient; to convert other metallic oxides present into sulfates. The mixture is heated,

while stirring, to between 230 C. and the temperature gradually increased to about 300 C; Ammonia, water vapor and silicon diammino tetrafluorideare evolved and collected. The silicon diammino tetrafluoride is converted into hydrated silica and ammonium fluoride by treating with ammonia water as described above. The hydrated silica is separated from the ammonium fluoride washed, and dried.

The ammonium fluoride solution is evaporated to crystallization and reused in the process. The condensed water from this evaporation is collected and used in the silica formation, as it contains ammonia.

The sulfate residue is lixiviated in boiling water; the solution is filtered from inso-lubles, principally calcium and iron salts, and ammonium alum is crystallized out by cooling. Iron salts, if present, may be eliminated by recrystallization.

The alum may be converted into aluminum hydroxide and ammonium sulfate by ammoma as described above. The ammonium sulfate may be reused after evaporation to crystallization as starting material for a further batch. When operating in this manner,the ammonium sulfate of the starting ingredients is substantially completely recovered. The only reagent consumed is the sulfuric acid necessary to convert the metals other than aluminum int-o sulfates, and this wastage is suitably replaced by introducing into the next char e an equivalent amount of ammonium sul ate to ether with the ammonium sulfate recovere This additional ammonium sulfate may be prepared by neutralizing the surplus ammonia with sulfuric acid.

Example I I furic acid and 1370 lbs. of ammonium fluoride. Considerable heat is generated and ammonia and water vapors are evolved.

The mixture is further heated under constant stirringfor 23 hours at about 250 C. The vapors evolved consisting principally of silicon diammino tetrafluoride, ammonia and water vapor are partiallycondensed whereby the silicon diammino tetrafluoride is separated from the ammonia and water vapor. Part of the ammonia is absorbed in water .to be used for precipitation of silica and regeneration of ammonium fluoride from the silicon diammino tetrafluoride, while another part is retained in the gaseous state to be used in the-conversion of aluminum sulfate into alumina.

, The sulfate residue is lixiviated in 900 gallons of hot water and filtered hot to prevent crystallization of alum, and the residue is 1,sea,oso

washed. The clear filtrate is cooled, alum crystallized out under constant stirring and dried in a centrifu drier. The mother liquor about 570 g ons, t ether with wash water from lixiv ation resi no is used in lixiviation of new batches of sulfates. The alum crystals are converted into aluminum h droxide and ammonium (and alkali) sul ate by action of ammonia gas, obtained from the first part of the process. As considerable heat is evolved water coolin is advisable.

While the invention as been described in connection with the details of specific examples thereof, it must be understoodthat I do not intend such details to be limitative of the invention except in so far as included in the terms of the appended claims.

I claim 1. The method of producing aluminum hydroxide which comprises treatin material containin alumina and silica wi um fluori e in substantially dry state, removing thesiljcon b volatilization from the material in the orm of ammonium silicon fluorine compounds, convertin alumina of said material into aluminum su fate and converting said aluminum sulfate compounds in the presence of residual fluoride compounds into aluminum h droxide.

2. The meth for roducin aluminum hydroxide which comprises treating material containin alumina and silica with ammonium fluoride in substantially dry state, removing silicon from said material by volatilization in the form of ammonium silicon fluorine compounds, converting alumina in said material into ammonium alum. in the presence of,

- residual fluoride compounds, and converting said ammonium alum into aluminum hydroxide. I

3. The method of producing aluminum hydroxide which comprises treatin material contain alumina and silicawith ammonum fluoride in substantially. d state, removin silicon from said material volatilization 1n the form of silicon fluori e ammonia, reacting upon the alumina with ammonium sulfate to form ammonium alum in the presence of residual fluoride com ounds, extracting ammonium alum from t e residue, and reacting upon said alum with ammonia to form aluminum hydroxide.

4. The method of producing aluminum hydroxide which comprises treatin material containing alumina and silica with ammonium fluoride in substantially dry state and removing the silicon of said material by volatilization in form of ammonium silicon fluoride com-pounds, converting alumina of said materi into aluminum sulfate compounds, crystallizin said sulfate compounds in the presence 0 residual fluoride compounds treating said crystals with ammonia as an separating the aluminum' hydroxide mtheaofiiblesubatancea.

ammonistate, removing silicon by volatilization in the form of siliconfluoride ammonia, reacting upon the alumina in said material with am -monium sulfate in the presence of residual fluoride compounds to formammonium alum, extracting and crystallizing said am monium alum, treating said crystals with ammonia gas, and separating the aluminum hydroxide from the soluble substances.

6. The cyclic process for producing aluminum hydroxide and hydrated silica from material containing alumina and silica which comprises treating said material with am= momum fluoride and ammonium sulfate, removing thesilicon by volatilization inrthe form of ammonium silicon fluorine compounds reacting upon said compounds with ammonia formed in said reaction and water thereby forming h drated silica and ammonium fluoride, col ecting ammonia evolved, dissolving and extractin the resulting aluminum sulfate compoun from the reaction mass, crystallizing and reacting upon said compounds with the ammonia evo ved and collected, separating the aluminum hydrate and ammonium sul ate formed thereb and using the recovered ammonium fluori e andammonium sulfate to react u on further quantities of material containing alumina state, heating said material with ammonium fluoride to form and volatilize the silicon as ammonium silicon fluorine compounds and treating the unvolatilized material with ammoniu'm sulfate insuflicient to convert theferrous compounds into normal sulfates, lixiviatin the esidue and crystallizing ammonium sum. erefrom, and reacting on said ammonium alum with ammonia to form aluminum hydroxide and ammonium sulfate.

V 8. In a c clic method for producing aluminum hy roxide reacting on material containin alumina and silica with ammonium fluori e and a reactive sulfate and subsequently reacting on the aluminum sulfate com minds with ammonia, incorporating in the initial reaction mass additional fluorspar and ammonium sulfate and maintaining a reaction temperature suitable for the reaction with the alumina and silica-containing material and not above 335 0., thereby securing substantially complete conversion of the fluorine content of thefluors er and supplementin the sire rtion of ,1? present.

.9, e me o of producing aluminum hydroxide which comprises treating material containing alumina and silica with ammonium fluoride in substantially dry state, removing the silicon by volatilization from the material in the form of ammonium silicon fluorine compounds, decomposing said compounds to release ammonia therefrom, converting alumina from the residue of said treatment into aluminum sulfate compounds, and contacting ammonia derived from the decomposition of the ammonium silicon fluorinecompounds, with said aluminum sulfate compounds to convert them into aluminum hydroxide. V

10. The method of producing aluminum hydroxide which comprises treating material containing alumina and silica with ammonium fluoride in substantially dry state, removin silicon-from said material by volatilization in the form of silicon fluoride ammonium compounds, decomposing said compounds with formation of ammonia, reactin upon the residue from said treatment wit ammonium sulfate to form ammonium alum in the presence of residual fluoride compounds and reacting upon said alum with ammonia derived from said decomposition to form aluminum h droxide.

In testimony w ereof I have hereunto set my hand this 30th day of Au ust, 1928.

SVEND s. VENDSEN.

CERTIFICATE OF CORRECTION.

Patent No. l, 889, 080;

November 29, .1932.v

SVEND S. SVENDSEN.

it is hereby certified that error appears in the printed specification of the above numbercdpatent requiring correction as follows:

Page 1, line 57, for

"fluoride ammonia" read "diammino tetrafluoride", and line 65, for"amomm|" read "amrnoniuml; page 2, line 100, for "plan" read "flow"; page 3, lim 43 and 44, claim" 3, -for "a'mmonum" read "ammonium"; and that lhefsaid Letters Patent should be read with these corrections therein'that the some may conform to the record oi the case in the Patent Office.

Signed and sealed this 21st day of February, A. D. 1933.

sen

M. 1. M00 Acting colmissiong' of Peter! nium fluoride in substantially dry state, removing the silicon by volatilization from the material in the form of ammonium silicon fluorine compounds, decomposing said compounds to release ammonia therefrom, converting alumina from the residue of said treatment into aluminum sulfate compounds, and contacting ammonia derived from the decomposition of the ammonium silicon fluorinecompounds, with said aluminum sulfate compounds to convert them into aluminum hydroxide. V

10. The method of producing aluminum hydroxide which comprises treating material containing alumina and silica with ammonium fluoride in substantially dry state, removin silicon-from said material by volatilization in the form of silicon fluoride ammonium compounds, decomposing said compounds with formation of ammonia, reactin upon the residue from said treatment wit ammonium sulfate to form ammonium alum in the presence of residual fluoride compounds and reacting upon said alum with ammonia derived from said decomposition to form aluminum h droxide.

In testimony w ereof I have hereunto set my hand this 30th day of Au ust, 1928.

SVEND s. VENDSEN.

CERTIFICATE OF CORRECTION.

Patent No. l, 889, 080;

November 29, .1932.v

SVEND S. SVENDSEN.

it is hereby certified that error appears in the printed specification of the above numbercdpatent requiring correction as follows:

Page 1, line 57, for

"fluoride ammonia" read "diammino tetrafluoride", and line 65, for"amomm|" read "amrnoniuml; page 2, line 100, for "plan" read "flow"; page 3, lim 43 and 44, claim" 3, -for "a'mmonum" read "ammonium"; and that lhefsaid Letters Patent should be read with these corrections therein'that the some may conform to the record oi the case in the Patent Office.

Signed and sealed this 21st day of February, A. D. 1933.

sen

M. 1. M00 Acting colmissiong' of Peter! 

